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Introduction: The adequacy of blood flow from the leptomeningeal collaterals is considered one of the most important factors determining the rate of infarct progression and response to acute stroke treatments in the setting of large vessel occlusions. Several patient-related variables, including age, vascular risk factors, and laboratory parameters, have been proposed to explain the interindividual variability of collateral flow among stroke patients. This study aimed to assess how pre-stroke frailty, an aging-related syndrome characterized by a loss in the physiologic reserve of numerous body functions, affected the degree of leptomeningeal collateral flow in the setting of acute ischemic stroke. Methods: A consecutive series of patients presenting with proximal middle cerebral artery occlusion were enrolled in this prospective, multicenter observational study. Collateral flow was determined by the regional leptomeningeal collateral (rLMC) score on admission computed tomography angiography images. Pre-stroke frailty was assessed by the Edmonton Frailty Scale (EFS), based on the information obtained from patients or their next of kin. The relationship between collateral flow and frailty was evaluated by bivariate and multivariate analyses taking into consideration the demographic, clinical, and imaging characteristics of the patients. Results: The study population was comprised of 116 patients (median [interquartile range] age 78 [71–84] years; 60% female). The EFS scores were negatively correlated with the rLMC score (r = −0.264; p = 0.004). A vulnerable or frail (EFS ≥6) status before stroke, higher blood pressure levels at admission, having imaging studies performed at an earlier phase after contrast injection, and presenting with thrombi extending to the proximal half of the M1 portion of the middle cerebral artery were significantly related to poor collateral circulation (rLMC score ≤10). After adjustment for potential confounders in multivariable analyses, a vulnerable/frail status was independently associated with poor leptomeningeal collateral flow (OR: 2.97 [95% CI: 1.15–7.69]; p = 0.025). Conclusion: Our findings highlight that the leptomeningeal collateral flow is also compromised as part of the diminished physiologic reserve characterizing the frailty status in patients with acute ischemic stroke. Future studies are needed to understand how this interplay contributes to the unfavorable clinical outcomes observed in frail patients after stroke. [ABSTRACT FROM AUTHOR]

Purpose of review: This narrative review summarized the major studies focusing on the association between revascularization therapies (intravenous thrombolysis and endovascular thrombectomy) and collateral circulation status in terms of outcome and safety. Our aim is to elucidate, drawing upon the latest scientific evidence, the pivotal role that collateral circulation plays in shaping the prognosis and potential therapeutic in patients with ischemic stroke. Recent findings: The data currently available suggest that pre-treatment assessment of collateral circulation may be crucial, as a good collateral circulation status appears to be associated with better outcomes in terms of both early revascularization and long-term disability. There is limited literature about the assessment of collateral circulation prior to acute reperfusion therapy. Summary: The role of the intracranial collateral circulation is gaining increasing attention in the field of ischemic stroke, both in terms of outcome prognosis and therapeutic interventions. These findings need to be confirmed by more structured randomized controlled trials (RCTs), but they suggest that investigating therapeutic strategies to maintain and support collateral circulation may represent the future of ischemic stroke therapy. [ABSTRACT FROM AUTHOR]

There is a growing recognition regarding the importance of pial collateral flow in the protection from impending ischemic stroke both in preclinical and clinical studies. Collateral flow is also a major player in sensory stimulation-based protection from impending ischemic stroke. Doppler optical coherence tomography has been employed to image spatiotemporal patterns of collateral flow within the dorsal branches of the middle cerebral artery (MCA) as it provides a powerful tool for quantitative in vivo flow parameters imaging (velocity, flux, direction of flow, and radius of imaged branches). It was employed prior to and following dorsal permanent MCA occlusion (pMCAo) in rat models of treatment by protective sensory stimulation, untreated controls, or sham surgery controls. Unexpectedly, following pMCAo in the majority of subjects, some MCA branches continued to show anterograde blood flow patterns over time despite severing of the MCA. Further, in the presence of protective sensory stimulation, the anterograde velocity and flux were stronger and lasted longer than in retrograde flow branches, even within different branches of single subjects, but stimulated retrograde branches showed stronger flow parameters at 24 h. Our study suggests that the spatiotemporal patterns of collateral-based dorsal MCA flow are dynamic and provide a detailed description on the differential effects of protective sensory stimulation.

Perfusion through leptomeningeal collateral vessels is a likely pivotal factor in the outcome of ischemic stroke patients. Acupuncture has been reported to restore cerebral blood flow (CBF) after acute ischemic stroke, but the underlying mechanisms are poorly understood. This study aimed to examine whether electroacupuncture (EA) could improve CBF following an acute ischemic injury by regulating leptomeningeal collaterals. The clinical outcomes suggest that EA resulted in an increase in the average CBF within the whole brain and gray matter of healthy subjects compared to pre-intervention. The experiments conducted on animals revealed that EA was able to improve neurological function, reduce infarct volume, and salvage tissue damage in the peri-infarct areas of permanent middle cerebral artery occlusion rats. Additionally, EA was found to increase cerebral perfusion and the diameter of developed leptomeningeal anastomoses, accompanied by activation of cholinergic neurons of the nucleus basalis of Meynert (NBM). However, these effects of EA were reversed by chemogenetic inhibition of cholinergic neurons in the NBM or by intraperitoneal injection of acetylcholine receptors antagonist atropine. These findings suggest that EA improved CBF after acute ischemic stroke, partially via activating cholinergic projections from the NBM to the cortex, thereby promoting leptomeningeal collateral circulation. ClinicalTrials.gov identifier: NCT03444896. [ABSTRACT FROM AUTHOR]

Abstract Background The hyperdense middle cerebral artery sign (HMCAS) is an early radiological marker to provide an early diagnosis and to identify ischemia. As reported, HMCAS is associated with heavy clot burden. Moreover, a heavy clot burden may cause obstruction of the orifices of arteries for leptomeningeal collateral flows and can lead to severe clinical conditions. However, the direct relationship between HMCAS and collateral flows remains unclear. Therefore, we explored the association between HMCAS and leptomeningeal collaterals in patients with acute ischemic stroke. Methods Consecutive ischemic stroke patients were enrolled from January 2015 to April 2021. HMCAS appearance and collateral status were detected by multimodal computed tomography at admission. Logistic regression analyses helped to identify the association between HMCAS, collateral flows and stroke severity. Results In 494 included patients, 180 (36.4%) presented with HMCAS. Ipsilateral collaterals were not seen or less prominent in patients with HMCAS (P

We investigated the association between cerebral small vessel disease (CSVD) and ipsilateral leptomeningeal collateral (LMC) status in patients with symptomatic intracranial atherosclerotic stenosis (sICAS). In 108 patients with 50–99% symptomatic intracranial internal carotid artery or M1 middle cerebral artery stenosis, 4 CSVD imaging markers (lacunes, cerebral microbleeds, enlarged perivascular spaces [EPVSs], and white matter hyperintensities [WMHs]) were assessed in MRI. Score of 0 or 1 was assigned to each marker and added up as a summary CSVD score (ranging 0–4) to reflect an overall CSVD burden. Ipsilateral LMC status was assessed by determining the laterality of distal vessels in anterior and posterior cerebral artery territories on CT angiography. Moderate-to-severe EPVSs (adjusted odds ratio [aOR] = 4.15; p = 0.031) and WMHs (aOR = 5.90; p = 0.010), and higher summary CSVD score (aOR = 1.66; p = 0.030) were independently associated with poor LMCs. There was significant interaction between stenosis percentage in sICAS and summary CSVD score on poor LMCs (p = 0.022 for interaction), when higher CSVD score was significantly associated with poor LMCs in patients with severe sICAS (aOR = 2.84; p = 0.011) but not in those with moderate sICAS. The findings indicated possibly adverse effect of CSVD on the recruitment or development of LMCs in sICAS patients, especially in patients with severe sICAS. [ABSTRACT FROM AUTHOR]

Background: The hyperdense middle cerebral artery sign (HMCAS) is an early radiological marker to provide an early diagnosis and to identify ischemia. As reported, HMCAS is associated with heavy clot burden. Moreover, a heavy clot burden may cause obstruction of the orifices of arteries for leptomeningeal collateral flows and can lead to severe clinical conditions. However, the direct relationship between HMCAS and collateral flows remains unclear. Therefore, we explored the association between HMCAS and leptomeningeal collaterals in patients with acute ischemic stroke.Methods: Consecutive ischemic stroke patients were enrolled from January 2015 to April 2021. HMCAS appearance and collateral status were detected by multimodal computed tomography at admission. Logistic regression analyses helped to identify the association between HMCAS, collateral flows and stroke severity.Results: In 494 included patients, 180 (36.4%) presented with HMCAS. Ipsilateral collaterals were not seen or less prominent in patients with HMCAS (P < 0.001). The HMCAS appearance was significantly associated with less collaterals (odds ratio 5.17, 95% confidence interval 3.27-8.18, P < 0.001), internal carotid artery + M1/M1 occlusion, the initial stroke severity and follow-up outcomes. Subgroup analyses further confirmed HMCAS as an indicator of poor collaterals in ischemic stroke (all P values < 0.05).Conclusions: HMCAS is associated with poor leptomeningeal collaterals, the stroke severity and a poor neurological outcome. Therefore, the HMCAS appearance can act as an early warning sign for healthcare professionals to be alert for poor collateral flows and poor neurological outcomes in ischemic stroke patients with middle cerebral artery occlusion. [ABSTRACT FROM AUTHOR]

Moyamoya disease (MMD) is characterized by bilateral, chronic progressive stenosis at the terminal portions of the internal carotid arteries and their proximal branches. The "smoke-like" appearance of the arterial collaterals in angiography gives the disease its name. The "ivy-sign" is the less-known magnetic resonance imaging (MRI) pattern of this disease. The leptomeningeal collaterals present as diffuse signal enhancement at the brain surface in contrast-enhanced T1-weighted image and fluid-attenuated inversion recovery sequences "as if overgrown with ivy." We report on three patients with MMD in whom the "ivy-sign" was already present but misinterpreted in the initial MRI of the brain. The correct diagnosis was made only after repeated MRI. Using three case studies, we describe the difficulties in the interpretation of the "ivy-sign" as an MRI pattern. Knowledge of the "ivy-sign" can be helpful, especially in diseases predisposing to MMD. If this MRI pattern is present, MMD should be considered and MR angiography should be added. [ABSTRACT FROM AUTHOR]

Recanalization is the mainstay of ischemic stroke treatment. However, even with timely clot removal, many stroke patients recover poorly. Leptomeningeal collaterals (LMCs) are pial anastomotic vessels with yet-unknown functions. We applied laser speckle imaging, ultrafast ultrasound, and two-photon microscopy in a thrombin-based mouse model of stroke and fibrinolytic treatment to show that LMCs maintain cerebral autoregulation and allow for gradual reperfusion, resulting in small infarcts. In mice with poor LMCs, distal arterial segments collapse, and deleterious hyperemia causes hemorrhage and mortality after recanalization. In silico analyses confirm the relevance of LMCs for preserving perfusion in the ischemic region. Accordingly, in stroke patients with poor collaterals undergoing thrombectomy, rapid reperfusion resulted in hemorrhagic transformation and unfavorable recovery. Thus, we identify LMCs as key components regulating reperfusion and preventing futile recanalization after stroke. Future therapeutic interventions should aim to enhance collateral function, allowing for beneficial reperfusion after stroke. [Display omitted] • LMCs maintain perfusion during stroke • Upon recanalization, LMCs allow for a gradual reperfusion • In mice with poor LMCs, recanalization causes deleterious hyperperfusion • Stroke patients with poor LMCs show fast reperfusion and futile recanalization Futile recanalization is a serious problem for stroke treatments. Binder and El Amki et al. demonstrate that leptomeningeal collaterals (LMCs) regulate reperfusion after stroke. Mice with poor LMCs developed rapid, uncontrolled hyperperfusion. In stroke patients, they found a similar deleterious reperfusion. Collateral function should be target of novel stroke treatments. [ABSTRACT FROM AUTHOR]

Prominent cortical vessels on susceptibility-weighted imaging (PCV–SWI) correlate with poor leptomeningeal collaterals. However, little is known about PCV–SWI in recanalization therapy-treated patients with anterior circulation large vessel occlusions (LVO). We investigated PCV–SWI-based assessment of leptomeningeal collaterals and outcome predictions in 100 such patients in an observational study. We assessed PCV–SWI using the Alberta Stroke Program Early CT Score and evaluated leptomeningeal collaterals on multiphase CT angiography (mCTA). Predictive abilities were analyzed using multivariable logistic regression and area of receiver operating curves (AUCs). The extent of PCV–SWI correlated with leptomeningeal collaterals on mCTA (Spearman test, r = 0.77; p < 0.001); their presence was associated with worse functional outcomes and a lower successful recanalization rate (adjusted odds ratios = 0.24 and 0.23, 95% CIs = 0.08–0.65 and 0.08–0.65, respectively). The presence of PCV–SWI predicted outcomes better than good collaterals on mCTA did (C-statistic = 0.84 vs. 0.80; 3-month modified Rankin Scale (mRS) 0–2 = 0.75 vs. 0.67 for successful recanalization). Comparison of AUCs showed that they had similar abilities for predicting outcomes (p = 0.68 for 3-month mRS 0–2; p = 0.23 for successful recanalization). These results suggest that PCV–SWI is a useful feature for assessing leptomeningeal collaterals in acute ischemic stroke patients with anterior circulation LVO and predicting outcomes after recanalization therapy.

Prognosis of patients with acute ischemic stroke is strictly related to the patency and prominence of the collateral leptomeningeal pathways distal to the arterial occlusion. The gold standard for assessment of collateral circulation is conventional angiography, but it is invasive and used in selected cases. To date, the most reliable technique is multiphase CTA; currently, the available classifications of collateral circles are often complex, time-consuming, and require a trained observer. The purpose of our work is to establish the effectiveness of a new semi-automatic post-processing software (ColorViz FastStroke, GE Healthcare, Milwaukee, Wisconsin) in evaluation of collateral circulation compared to the six-point classifications of multiphase CTA already validated in literature. We selected 86 patients with anterior ischemic stroke symptoms who underwent multiphasic CTA in our emergency department. Two radiologists separately evaluated the collateral leptomeningeal vessels, analyzing respectively, the multiphase CTA (using the six-point scale and its trichotomized form) and ColorViz (using a three-point scale). Then the results were matched. We found a good correlation between the two different analyses; the main advantage of ColorViz is that, while maintaining fast diagnostic times, it allows a simpler and more immediate evaluation of collateral circulation, especially for less experienced radiologists.

Background: The objective of this study was to investigate the prognostic value of computed tomographic angiography (CTA) based on leptomeningeal collateral (LMC) status and other parameters in acute ischemic stroke (AIS) patients with internal carotid artery (ICA) terminus occlusion treated with endovascular treatment (EVT).Methods: All eligible patients from January 2013 to December 2017 undergoing EVT were retrospectively reviewed. The regional leptomeningeal score was used to assess the LMCs on baseline CTA. The collateral status measured by the LMC score (0-20) was trichotomized into 3 groups: good (17-20), intermediate (11-16), and poor (0-10).Results: Our sample included a total of 119 eligible patients (60 males; mean age, 73 years) with a median baseline National Institute of Health Stroke Scale (NIHSS) score of 14. Patients with a good LMC score had a lower baseline mean NIHSS score, a higher mean Alberta Stroke Program Early CT score, and a higher mean clot burden score (CBS). Baseline NIHSS score <15 (odds ratio [OR] 3.69 95% confidence ratio [CI]: 1.32-10.29, P = .013), CBS ≥ 6 (OR 3.97 95%CI: 1.05-14.99, P = .042), good LMC score (OR 5.14 95%CI: 1.62-16.26, P = .005) and successful recanalization (OR 11.55 95%CI: 2.72-48.99 P = .001) were independent predictors of good clinical outcomes.Conclusions: CTA-based LMC status and CBS are powerful predictors of clinical outcomes in patients with an acute ICA terminus occlusion treated with EVT. [ABSTRACT FROM AUTHOR]

A 2-year old girl referred to our department with complaint of transient ischemic attack and right sided hemiparesis, was investigated with contrast enhanced MRI Brain and time of flight MRA and diagnosed as moyamoya disease with ivy sign. The ivy sign is a Magnetic resonance imaging (MRI) finding observed both in post contrast T1-weighted images (T1WI) and Fluid attenuated inversion recovery (FLAIR) images due to the development of leptomeningeal collateral and pial network. Moyamoya disease is a progressive multifocal occlusive arteriopathy of unknown origin and is an infrequent cause of cerebrovascular accident in children. The patient was treated conservatively and referred to a higher centre for specific neurosurgical revascularization surgery which has favorable outcome but because of his family disagreement cerebral revascularization surgery was not performed. [ABSTRACT FROM AUTHOR]

Introduction: Intracranial artery-to-artery antegrade revascularization is a poorly recognized entity, more so when it involves main stem arteries. The etiology, appearance, and significance of this condition are not described in the literature. Case presentation: We describe a case of spontaneous revascularization of a chronically occluded middle cerebral arterial branch by collaterals from the proximal segment reconstituting distal flow, mimicking a brain arteriovenous malformation in a 9-year old boy. We discuss the nature of these channels, presumed to be related to artery to artery collaterals that are either dilated adventitial vasa vasorum, or, more likely, leptomeningeal collaterals that are hypertrophied in response to cerebral demand. We review the literature regarding intracerebral vasa vasorum and leptomeningeal collaterals including their imaging. Conclusion: Recognizing the tortuous channels associated with this type of vascular abnormality as normal vessels reconsituting distal flow may prevent unnecessary and potentially dangerous treatments. [ABSTRACT FROM AUTHOR]

Introduction: Various clinical and radiologic variables impact the neurologic prognosis of patients with ischemic cerebrovascular accidents. About 30% of ischemic cerebrovascular accidents are caused by proximal obstruction of the anterior circulation; in these cases, systemic thrombolysis is of limited usefulness. CT angiography is indicated in candidates for endovascular treatment. Various radiologic factors, including the grade of leptomeningeal collateral circulation, as well as the length, density, and extension of the thrombus, have been identified as predictors of neurologic prognosis after anterior ischemic cerebrovascular accidents due to proximal vascular obstruction. Final infarct volume correlations with mortality and long-term functional outcome in these patients. This study aimed to determine the best predictors of final infarct volume on CT angiography in patients with ischemic cerebral accidents due to proximal occlusion., Materials and Methods: This retrospective observational study included adults with ischemic cerebrovascular accidents due to obstruction of the anterior circulation diagnosed by CT angiography in the period comprising June 2009 through December 2019. We measured the length and density of the thrombus in unenhanced CT images, and we used the clot burden score to record the grade of leptomeningeal collateral circulation and the extension of the thrombus. Then we measured the final infarct volume on follow-up CT and analyzed the correlations among these radiologic factors in the infarct volume., Results: We included 54 patients [mean age, 82 y; 41 (75%) women] with ischemic cerebrovascular accidents due to proximal occlusion. About 60% of the cerebrovascular accidents affected the right cerebral hemisphere, and the most commonly affected vessel was the M1 segment of the medial cerebral artery (40.7%). Final infarct volume correlated with the grade of leptomeningeal collateral circulation (p=0.03) and with the clot burden score (p=0.01). Neither the length nor the density of the thrombus correlated with final infarct volume., Conclusion: The final infarct volume can be estimated on the initial CT angiogram. Nevertheless, we found no useful predictive factors in unenhanced CT images. The best independent radiologic predictors of the final infarct volume are the grade of collateral circulation and the clot burden score, especially in patients who did not undergo mechanical thrombectomy, because mechanical thrombectomy improves outcomes. These factors are important for decision making in the management of patients with ischemic cerebrovascular accidents due to proximal occlusion., (Copyright © 2022 SERAM. Published by Elsevier España, S.L.U. All rights reserved.)

Purpose Clinically successful endovascular therapy ( EVT) in ischemic stroke requires reliable noninvasive pretherapeutic selection criteria. We investigated the association of imaging parameters including CT angiographic collaterals and degree of reperfusion with clinical outcome after EVT. Methods In our database, we identified 93 patients with large vessel occlusion in the anterior circulation treated with EVT. Besides clinical data, we assessed the baseline Alberta Stroke Program Early CT score ( ASPECTS) on noncontrast CT ( NCCT) and CT angiography ( CTA) source images, collaterals ( CT- CS) and clot burden score ( CBS) on CTA and the degree of reperfusion after EVT on angiography. Three readers, blinded to clinical information, evaluated the images in consensus. Data-driven multivariable ordinal regression analysis identified predictors of good outcome after 90 days as measured with the modified Rankin Scale. Results Successful angiographic reperfusion ( OR 26.50; 95%- CI 9.33-83.61) and good collaterals ( OR 9.69; 95%- CI 2.28-59.27) were independent predictors of favorable outcome along with female sex ( OR 0.35; 95%- CI 0.14-0.85), younger age ( OR 0.88; 95%- CI 0.83-0.92) and higher NCCT ASPECTS ( OR 2.54; 95%- CI 1.01-6.63). Outcome was best in patients with good collaterals and successful reperfusion, but there was no statistical interaction between collaterals and reperfusion. Conclusions CTA-collateral status was the strongest pretherapeutic predictor of favorable outcome in ischemic stroke patients treated with EVT. CTA-collaterals are thus well suited for patient selection in EVT. However, the independent effect of reperfusion on outcome tended to be stronger than that of CTA-collaterals. [ABSTRACT FROM AUTHOR]

Background: We explore the role of dural sinus morphology, leptomeningeal collaterals, and clot localization in the development of malignant brain edema in acute ischemic stroke in anterior circulation.Methods: This is a single-center retrospective study of consecutive stroke patients with acute occlusion (middle cerebral artery M1 ± intracranial internal carotid artery) treated with intravenous thrombolysis (from November 2009 to November 2014). Admission computed tomography angiography data were evaluated for hypoplasia of dural sinuses, leptomeningeal collaterals, and clot location. Primary outcome was midline shift (<5 mm versus ≥5 mm) on follow-up computed tomography. Secondary outcomes were infarct volume and modified Rankin Scale score of 2 or lower at 90 days. Multivariate logistic regression was used.Results: Of 86 patients (49 females), 36 (42%) had poor collaterals, 26 (30%) had ipsilesional sinus hypoplasia, and 38 (44%) had proximal clots. A midline shift of 5 mm or higher was diagnosed in 14 patients (16%). Infarct volume was larger in the group with midline shift (median: 318 mL [interquartile range {IQR} = 260-350]) than in the group without midline shift (median: 44 mL [IQR = 28-60]) (P = .007). In multivariate analysis, poor leptomeningeal collaterals (odds ratio [OR] = .11, 95% confidence interval [CI] = .03-.44, P = .002 for good collaterals) and ipsilesional sinus hypoplasia (OR = 6.43, 95% CI = 1.5-46.1, P = .008) were independently associated with a midline shift of 5 mm or higher.Conclusion: Patients with poor leptomeningeal collaterals and ipsilesional hypoplasia of dural sinuses are more likely to develop midline shift. [ABSTRACT FROM AUTHOR]

Cerebral collaterals are vascular redundancies in the cerebral circulation that can partially maintain blood flow to ischemic tissue when primary conduits are blocked. After occlusion of a cerebral artery, anastomoses connecting the distal segments of the MCA with distal branches of the ACA and PCA (known as leptomeningeal or pial collaterals) allow for partially maintained blood flow in the ischemic penumbra and delay or prevent cell death. However, collateral circulation varies dramatically between individuals, and collateral extent is significant predictor of stroke severity and recanalization rate. Collateral therapeutics attempt to harness these vascular redundancies by enhancing blood flow through pial collaterals to reduce ischemia and brain damage after cerebral arterial occlusion. While therapies to enhance collateral flow remain relatively nascent neuroprotective strategies, experimental therapies including inhaled NO, transient suprarenal aortic occlusion, and electrical stimulation of the parasympathetic sphenopalatine ganglion show promise as collateral therapeutics with the potential to improve treatment of acute ischemic stroke. [ABSTRACT FROM AUTHOR]

Background: Moyamoya disease is a chronic progressive cerebrovascular disease with a complex pathophysiology and unique features of neoangiogenesis. These features are still known only to a few specialists, although they determine clinical course and outcomes of disease., Objective: To determine the nature and degree of neoangiogenesis in restructuring the natural collateral circulation in patients with moyamoya disease and its effect on cerebral blood flow. The influence of collateral circulation on postoperative results and factors of its effectiveness will be analyzed in the 2 nd part of the study., Material and Methods: The study included 65 patients with moyamoya disease who underwent preoperative selective direct angiography with separate contrast enhancement of both internal, external and vertebral arteries. We analyzed 130 hemispheres. Suzuki stage of disease, pathways of collateral circulation and their relationship with reduction of cerebral blood flow and clinical manifestations were assessed. Distal vessels of the middle cerebral artery (MCA) were additionally studied., Results: Suzuki stage 3 was the most common (36 hemispheres, 38%). Leptomeningeal collaterals were the most common among intracranial collateral tracts (82 hemispheres, 66.1%). Extra-intracranial transdural collaterals were found in half of the cases (56 hemispheres). We observed certain changes in distal vessels of the MCA (hypoplasia of M3 branches) in 28 (20.9%) hemispheres. Suzuki stage of disease significantly determined degree of cerebral blood flow insufficiency, i.e. more severe perfusion deficit was observed at the later stages of disease. A well-developed system of leptomeningeal collaterals significantly reflected stages of compensation and subcompensation of cerebral blood flow according to perfusion data (χ 2 =20.394, p <0.001)., Conclusion: Neoangiogenesis is a natural compensatory mechanism in moyamoya disease designed to maintain brain perfusion under reduced cerebral blood flow. Predominant intra-intracranial collaterals are associated with ischemic and hemorrhagic events. Timely restructuring on extra-intracranial ways of collateral circulation prevents adverse manifestations of disease. Assessment and understanding of collateral circulation in patients with moyamoya disease create the prerequisites for substantiating the method of surgical treatment.